Patients on chronic stimulant therapy for the treatment of Attention deficit hyperactivity disorder (ADHD) who are undergoing an outpatient surgical or diagnostic procedure will be randomized to one of two groups: stimulant medication administered on the day of surgery or stimulant medication withheld on the day of surgery. The choice of anesthetic pharmacology will be at the discretion of the attending anesthesiologist, but the endpoint will be a bispectral index (BIS) between 40 and 60 to ensure adequate and similar depth of anesthesia. Blood pressure, heart rate and use of vasopressors or anticholinergics will be recorded and the incidence of hypotension, bradycardia, or administration of medications will be compared between the two groups.